In the baking industry it is an important objective to provide bread products which have a soft crumb structure, a high specific volume and which are not prone to staling within the desirable shelf life for fresh bread products.
One prerequisite for obtaining bread products having such a desired quality is the provision of a dough having appropriate rheological and structural characteristics. In this connection, the “strength” or “weakness” of doughs is an important aspect of making farinaceous finished products from doughs, including baking. The “strength” or “weakness” of a flour dough is primarily determined by the protein content of the flour and in particular, the content and the quality of the gluten protein is an important factor in that respect. Flours with a low protein content is generally characterized as “weak”. Thus, the cohesive, extensible, rubbery mass which is formed by mixing water and weak flour will usually be highly extensible when subjected to stress, but it will not return to its original dimensions when the stress is removed.
Flours with a high protein content are generally characterized as “strong” flours and the mass formed by mixing such a flour and water will be less extensible than the mass formed from a weak flour, and stress which is applied during mixing will be restored without breakdown to a greater extent than is the case with a dough mass formed from a weak flour.
Strong flour is generally preferred in most baking contexts because of the superior rheological and handling properties of the dough and the superior form and texture qualities of the finished baked or dried products made from the strong flour dough.
Within the bakery and milling industries it is known to use dough “conditioners” to strengthen the dough. Such dough conditioners are normally non-specific oxidizing agents such as e.g. iodates, peroxides, ascorbic acid, K-bromate or azodicarbonamide and they are added to dough with the aims of improving the baking performance of flour to achieve a dough with improved stretchability and thus having a desirable strength and stability. The mechanism behind this effect of oxidizing agents is that the flour proteins, in particular gluten contains thiol groups which, when they become oxidized, form disulphide bonds whereby the protein forms a more stable matrix resulting in a better dough quality and improvements of the volume and crumb structure of the baked products.
However, the use of several of the currently available oxidizing agents is either objected to by consumers or is not permitted by regulatory bodies and accordingly, it has been attempted to find alternatives to these conventional flour and dough additives and the prior art has i.a. suggested the use of glucose oxidase for this purpose.
Thus, U.S. Pat. No. 2,783,150 discloses the addition of glucose oxidase to flour to improve dough strength and texture and appearance of baked bread. CA 2,012,723 discloses bread improving compositions comprising cellulolytic enzymes such as xylanases and glucose oxidase, the latter enzyme being added to reduce certain disadvantageous effects of the cellulolytic enzymes (reduced dough strength and stickiness) and it is disclosed that addition of glucose to the dough is required to obtain a sufficient glucose oxidase activity.
EP-B1-321 811 discloses the use of an enzyme composition comprising glucose oxidase and sulfhydryl oxidase in combination to improve the rheological characteristics of doughs. It is mentioned in this prior art document that the use of glucose oxidase alone has not been successful.
In EP-B1-338 452 is disclosed an enzyme composition for improving dough stability, comprising a mixture of cellulase/hemicellulase, glucose oxidase and optionally sulfhydryl oxidase.
However, the use of glucose oxidase as a dough improving additive has the limitation that this enzyme requires the presence of sufficient amounts of glucose as substrate in order to be effective in a dough system and generally, the glucose content in cereal flours is low. Therefore, the absence of glucose in doughs or the low content hereof in doughs will be a limiting factor for the effectiveness of glucose oxidase as a dough improving agent. Thus, it may be required to add sucrose or glucose as substrate to the dough to obtain a sufficient effect and glucose oxidase does not constantly provide a desired dough or bread improving effect when used alone without the addition of other enzymes.
Recently, it has been suggested to use hexose oxidase for improving the quality of flour dough (WO 96/39851).
Cellulases and/or hemicellulases (hemicellulases are also referred to herein as pentosanases or xylanases) which cleave non-starch polysaccharides contained in flour are used as a means of improving bread quality. The cleavage of glycosidic bonds in the non-starch polysaccharides affects the water retention and water binding capacity, viscosity and proofing capacity of the dough as well as the texture, aroma, taste and freshness of the bread. Generally speaking, the use of cellulases/hemicellulases gives an improved oven spring to the dough and an improved bread volume, grain structure and anti-staling properties to the finished bakery product.
However, the use of cellulases or hemicellulases involve certain undesirable side effects. In particular, it is commonly observed that the addition of these enzymes to doughs results in that the doughs become too slack and sticky, which may cause problems. It is therefore necessary to use dosages of cellulases or hemicellulases which are too low for an optimum baking result to be achieved, so that the enzymes in question cannot be utilized to the full extent. At low dosage level, cellulases or hemicellulases make the mechanical handling of the dough easier whereas the effect of such enzymes on the process tolerance (dough stability) may be insufficient when used alone and accordingly, emulsifiers have to be used as additives.
It has now been found that the above problems associated with the use of cellulases or hemicellulases in flour doughs can be reduced or prevented by using these enzymes in combination with an oxidoreductase such as galactose oxidase under conditions where sufficient substrate for the latter enzyme is present in the dough. Therefore, by using such a combination of enzymes it has become possible to achieve the maximum effect of cellulases or hemicellulases, including the use of these enzymes in high amounts in doughs without the occurrence of stickiness and/or slackness herein.
Being an oxidoreductase, galactose oxidase will, in addition to the above effects, provide the dough strengthening effect and thereby improve the rheological characteristics of flour doughs as a result of formation of disulphide bonds in S-containing amino acids and also, as it was demonstrated by the inventors, as the result of binding ferulic acid binding to other ferulic acid moieties.
Galactose oxidase (D-galactose:oxygen 6-oxidoreductase, EC 1.1.3.9) is an enzyme which in the presence of oxygen is capable of oxidizing galactose to the corresponding lactone, D-galacto-hexodialdose with subsequent hydrolysis to the aldobionic acid. Accordingly, the oxidation catalyzed by galactose can be illustrated as follows:D-Galactose+O2→γ-D-galacto-hexodialdose+H2O2
However, the natural content of galactose or other oxidizable substrates for galactose oxidase in cereal flours is very low, typically in the range of 0.001 to 0.01 wt %. Practical use of that enzyme in a flour based dough is therefore not possible without providing in the dough a sufficient amount of oxidizable substrates for the enzyme.